SCEC Award Number 16096 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Depth Dependent In Situ Crustal Stress Models With Implications For Fault Strength In Southern California
Name Organization
Karen Luttrell Louisiana State University Bridget Smith-Konter University of Hawaii at Manoa
Other Participants LSU undergraduate student researcher
SCEC Priorities 2d, 1b SCEC Groups SDOT
Report Due Date 03/15/2017 Date Report Submitted 07/02/2017
Project Abstract
We have extended our previous models of in situ crustal stress, with orientation derived from inverted focal mechanisms and a magnitude estimated as that required to overcome resistance from topography, to include depth dependence from topography, and have created a framework for including 4-D fault loading stress over several earthquake cycles. The preliminary results indicate stress increases with depth, as expected, to a maximum in the seismogenic zone of ~62 MPa differential stress in the areas of most rugged topography. We have also developed a framework to resolve a given stress field onto Community Fault Model planes to estimate sustained normal and shear stress magnitude. These results can be used to investigate variations in fault strength with depth and throughout the plate boundary system. The code for conducting this analysis will be made available to the SCEC community as part of the new CXM modeling efforts. Finally, we have investigated prospects for extending direct observations of stress state from boreholes, by searching through ~2500 historic industry-collected well logs from California, from a proprietary database accessible by students at Louisiana State University. From the available logs, we identified one with information from oriented logging tools that could be used to ascertain stress azimuth, and subsequently continued our analysis of stress orientations indicated by different observation techniques.
Intellectual Merit These findings directly support an important objective of SCEC and the CSM, to synthesize the insights offered by diverse contributed models in order to gain a more holistic understanding of the 4D stress field and be better situated to present a community-endorsed stress model to the broader SCEC community. Our investigations have developed novel estimates of stress magnitude and established novel techniques to infer the near-fault character of the tectonic driving stress and explore the relative importance of locked faults on the in situ stress state.
Broader Impacts This project has enabled one LSU undergraduate student to conduct research on southern California stress state and gain valuable experience in data mining, computer programming, figure preparation, and writing skills. This research was presented at the 2016 SCEC Annual Meeting.
Exemplary Figure Figure 2: a) minimum magnitude () of stress field required to overcome the load of topography in the crust, at 5 km depth. This metric is equivalent to the maximum shear stress on an optimally oriented plane, for a given stress tensor. b) maximum shear stress from depth dependent minimum stress field estimate resolved onto the planes of the Community Fault Model [Plesch et al., 2007; Nicholson et al., 2013]. Each point represents the centroid of a CFM fault patch triangle c) same as b), focused on the SAF, SJF, and Banning segments (black box in b). d) 3-D view of region shown in c). Note the depth dependence of resolved stress estimates on various fault segments.